Analog Printing Knowledge
Analog

Photomechanical (Analog) Proof

An analog proof requires that film negatives or positives be made in order to produce the color proof. Analog proofs can be categorized as either an "analog position proof" or an "analog contract proof".

An analog position proof provides an overall concept of the color scheme for the project, as well as the design format. Because the colors that are used to make the proof do not coincide with the colors utilized with the printing device, it is never used as a guide to match the color with the final printed piece.

The analog contract proof is used as the final version approved by the customer, in which the colors of the final proof are expected to match. The analog process utilizes film negative color separations of the primary subtractive color components of the image (cyan, magenta, yellow) and black. The separations in turn are used to create separate layers containing colored toners (color key) that match closely with the primary ink colors used when printing the project. The individual layers are sandwiched together to produce the full color effect. The separation negatives are also used to create the printing plates.

Analog proofs come in several types:

  • Blue Line - Sometimes called a Dylux, it is a one-color proof made from all four separation films. It is used to check the imposition, text, layout, and traps, but it is not used for checking color. Most systems use a vacuum frame to hold the film or flat in contact with the light-sensitive coated sheet. An ultraviolet light source then exposes the emulsion to create the image. There is no processing involved. It can be folded, trimmed and stitched to approximate the finished job. The proof is bluish in color, and the image fades with time.

  • Composite Overlay Proof - One of the trade names for a composite overlay proof is Color Key™ (Kodak). Each layer is a separate color overlaying each other. The colored layers usually represent the color separations (cyan, magenta, yellow, and black) and/or any spot colors. Most systems use a vacuum frame to hold the film layers or flats in contact with the light-sensitive coated sheet. The light source exposes the emulsion and the product is then processed. This process occurs for each color layer. The layers are taped down to any stock to be registered with the other layers and are usually put into the order in which they will be printed at the press. The composite overlay proof can be useful for checking color breaks, trapping, text, and layout, but it is not as good as other types of proofs for matching color at the press. The illustration below shows how four layers, representing the process colors, are taped down so that the individual layers can be registered.

  • Composite Integral Proofs

    • Precoated Subtractive - An example of a precoated subtractive proof is MatchPrint™ (Kodak). A negative for each color is placed on a laminated color sheet receiver stock, exposed to ultraviolet light, and then processed. A precoated subtractive proof can take about 30 minutes to produce. Consistent densities, dot gain, and color are the main advantages of this type of proof.

    • Additive - An example of an additive proof is Cromalin (DuPont). An additive proof is made by hand-mixing powdered toners into "recipes" for each color. The toners are available in color kits that can be used to create many pantone colors. If you do not want to mix toners to create the pantone color you need, you can order individual pantone colors from Dupont. The toners are also available in metallic and fluorescent colors. The proofs are prepared by adhering a clear photosensitive sheet onto a substrate, exposing the material with the film. After exposure the clear laminate is peeled from the base substrate leaving exposed adhesive. The adhesive then accepts the powdered toner which is applied and brushed off by hand. This process is repeated for each color and can be made on any stock. An additive proof takes about 30 minutes to produce.

      The advantages of an additive proof are: there is not a limit on the number of colors that can be used, you have the ability to mix your own colors, and you may apply any density that you desire. The main disadvantage is the inability of the colors to be consistent. The inconsistency is due to the hand mixing of the colors, which may cause a slight variance in the colors each time they are mixed.

Some types of analog proofs can show spot colors (PMS) and can be produced with different types of paper so that the result is a closer match to the final piece. Analog proofs will also show the line screen and screen angles in the film. Problems such as moiré patterns may also be present.

Consistency with any type of analog proof depends on the calibration of the proofing system and by using color bars on every proof. Even with current digital technology, traditional analog proofing is still the dominate method of color proofing, although digital proofing is quickly growing in acceptance.

Tips for checking an analog proof for accuracy

 


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